Interaction of CD40L with its receptor CD40, which is constitutively expressed by B cells and macrophages, is involved in both humoral and cellular immune responses and in essence links both types of immune responses. CD40L is expressed on <1% of human CD4+ T cells from normal controls, but on <17% of CD4+ T cells from active SLE patients. Persistent expression of CD40L has been reported on T cells of lupus patients by several groups. Upregulation of CD40 expression has also been observed in renal biopsy specimens from patients with proliferative but not membranous lupus nephritis. It has also been demonstrated that antibodies to CD40L ameliorate nephritis in several animal models of lupus. Objectives 1. To further delineate the role of CD40L-CD40 interaction between T cells and macrophages/mesangial/tubular epithelial cells in the pathogenesis of lupus nephritis. 2. To examine the therapeutic activity of anti-CD40L therapy in patients with lupus nephritis. 3. To examine the impact of anti-CD40L therapy on cellular interactions between T cells and other cells, and autoantibody production. 4. To study the natural history of lupus nephritis treated with different immunosuppressive regimens and to examine their long- term toxicity and efficacy. 5. To develop improved outcome criteria and/or surrogate markers to be used for future trials of lupus nephritis. 6. To collect DNA from patients and their parents for studies of lupus nephritis susceptibility and severity genetic markers. 7. To study the biology of FcgR in mononuclear phagocytes and renal mesangial cells in lupus nephritis by: a) examining the binding, endocytosis and processing of immune complexes as well as the biologic response of mononuclear and mesangial cells, and b) correlating binding/response with polymorphisms of the FcRg-chain. Results 1. Role of CD40-CD40L Interactions In co-culture experiments, CD40L activated peripheral blood monocytes stimulated human mesangial cells to produce chemotactic cytokines (MCP-1, RANTES) and cell adhesion molecules (ICAM-1). Both soluble factors (TNF-a, IL-1b) and cell contact via the b-2 integrins LFA-1 and Mac-1 are involved in this process. In on-going experiments normal monocytes are being compared to monocytes from lupus patients. Normal mesangial cells are also being compared to mesangial cells grown from lupus nephritis kidney biopsy specimens. 2. Anti-CD40L Therapy A multicenter study sponsored by Biogen, Inc. has been initiated with NIH as one of the 3 leading centers. The study will involve 115 patients and is expected to be completed in 2 years. 3. Natural History and Outcome Criteria The traditional end points of lupus nephritis (end-stage renal disease, doubling of serum creatinine or remission) require long periods of follow-up and a large number patients to demonstrate differences among treatment groups. Our current efforts involve analysis of data obtained during previous studies to improve outcome criteria and/or identify surrogate markers. Patients participating in our most recent randomized trial of immunosuppressive drugs have participated in a comprehensive evaluation of long term morbidity (associated with both disease and with therapy) and efficacy. 4. Genetic Markers for Susceptibility/Severity We have collected DNA from over 140 patients with lupus nephritis as well as from 26 parents of these patients. These samples will be used for studies to identify the role of putative genetic markers in determining susceptibility to disease, its severity and its response to therapy. Based on a study showing that the DD polymorphism of angiotensin converting enzyme (ACE) predicts severity and response to therapy in patients with IgA nephropathy (another immune complex mediated renal disease), we examined the role of ACE genotypes in lupus nephritis. African Americans with lupus nephritis, but not normal African Americans, were found to have a decreased prevalence of the DD genotype. This genotype has been associated with adverse cardiovascular and renal events. There was no difference in DD genotype distribution among Caucasians with lupus nephritis. 5. Role of Fcg Receptors. To date, we have collected elutriated monocytes from 7 patients with lupus nephritis and 15 normal donors. In addition, we have established mesangial cell lines from 2 lupus patients and 4 non-lupus nephrectomy specimens obtained from anatomic pathology. We have detected tyrosine phosphorylation of multiple intracellular proteins in these cell lines when stimulated with human IC. This is associated with production of cytokines which is our biologic read out assay. Morever, we have established a PCR based assay to detect polymorphisms of the g-chain. If we establish a link between such polymorphisms and altered receptor function we will then examine their prevalence in our lupus nephritis cohort and correlate it with severity of renal disease. Our studies are aimes at a) identifying the role of a molecule called CD40 ligand in injuring the kidney of patients with lupus and b) the response of kidneys to deposition of immune complexes. To this end, we use molecules which interfere with function of CD40 ligand (anti-CD40 ligand antibodies) and examine their effects in patients with lupus nephritis. Moreover, we grow cells from kidney biopsies of these patients and examine their ?behavior? in the test tube. Finally, we monitor a group of over 150 lupus patients that have participated in studies on the treatment of lupus nephritis in an effort to better understand the course of the disease and the long- term side effects of treatment.